core: Remove GenericChan/Port from prelude. Closes #4762

Author: z0w0

src/libcore/prelude.rs

@@ -34,7 +34,6 @@ pub use path::GenericPath;
 pub use path::Path;
 pub use path::PosixPath;
 pub use path::WindowsPath;
-pub use pipes::{GenericChan, GenericPort};
 pub use ptr::Ptr;
 pub use str::{StrSlice, Trimmable, OwnedStr};
 pub use to_bytes::IterBytes;